In a packet switching system comprising a large number of switching networks, it is desirable to monitor the delay introduced during the transmission of packets through each switching network. The delay monitoring allows system administration to identify routes which are experiencing long delays and to use alternate routes for new packet calls being set up within the packet system. In prior art systems which utilized a general purpose computer as the centralized, or main switching, element, the same computer could also have performed the delay calculations. However, in a packet switching system as disclosed in the above-identified applications, the switching of packets within each switching network is performed by distributed hardware. For example, the J. S. Turner, U.S. Pat. No. 4,494,230, "A Fast Packet Switching Network", describes a system comprising fast packet switching nodes interconnected by high-speed digital transmission links with each link being terminated on both ends by interface facilities.
A communication path is set up through the fast packet switching system by initially routing a call setup packet from an originating terminal to each central processor controlling a switching node in the route to the destination terminal. That packet precedes all other packets of the packet call. Each central processor is responsive to a receipt of the setup packet to store logical to physical address translation information in memories of its associated interface facilities, or trunk controllers. Thereafter, the central processor involvement in the communication of all subsequent packets for the message of that call is virtually eliminated. The physical address defines a path through the switching network of the switching node to an output trunk controller in the communication path to the destination terminal.
Upon receipt of a message packet from a link, a trunk controller utilizes its memory information for the assemblage of a new packet containing the physical address plus the originally received message packet. The trunk controller then sends the new packet to the switching network which in turn routes the new packet to the output trunk controller.
Since the central, or main, processor does not handle each individual packet in the Turner fast packet switching system, there exists a need for techniques which can accurately perform the delay monitoring functions. The monitoring should desirably introduce minimal delay into the switching of packets.
One of the aforementioned cases dealing with the Turner switching system, W. A. Montgomery, Ser. No. 392,377, relates to a time stamping arrangement in a trunk controller for accumulating the time taken by an individual packet to transverse a total packet switching system. No structure is disclosed in that case for providing the delay monitoring function in accordance with the subject matter of this case.